1. Field of the Invention
The present invention relates to a semiconductor device; more particularly, relates to replacing Au with Cu in an ohmic contact layer and a metal interconnect of a related compound semiconductor made of GaAs or InP.
2. Description of the Prior Art
A traditional compound semiconductor device (of an HBT (Heterojunction Bipolar Transistor) structure or a HEMT (High-Electron-Mobility transistor) structure) uses Au for an ohmic metal layer and a metal interconnect. Concerning RC delay, Cu can be used to replace Au with a lower resistance and a better heat dissipation for a better compound semiconductor device. As stated in the U.S. Pat. Nos. 6,444,567 and 6,319,819, a Cu production is obtained by a Cu CMP (Chemical Mechanical Polishing) and an obstruction between Cu and a dielectric layer. In the U.S. Pat. No. 6,455,425, a Cu production is obtained by a selective deposition of a Cu CMP planarization and an obstruction between Cu and a dielectric layer. In the U.S. Pat. No. 6,452,276, an alpha-wolfram is used as a diffusion barrier to Cu; and, in U.S. Pat. Nos. 6,437,440 and 6,291,885, a TaN. In the U.S. Pat. No. 6,180,523, Cu/Au interconnects are made in an eletronless way while its adhering layer is made of Ni, Al, polysilicon or PdSix and its diffusion barrier is made of Ni—B compound, Ni, Pd or Co, having a plug of Au or Cu.
In Taiwan, a prior art for Cu production uses a TaN plated by electroplating as a diffusion barrier and a metal damascene on silicon by CMP. Another prior art obtains a dual damascene of metal on a silicon layer by electroplating. Still another prior art uses a metal plasma sputtering process to plate Ti and uses CVD (Chemical Vapor Deposition) and MOCVD (Metal Organic Chemical Vapor Deposition) to deposit TiN as a diffusion barrier to Cu.
Yet, the above prior arts are for silicon productions only and use a complex Cu dual damascene or a CMP process, which are not for the production of compound semiconductor. So, the prior arts do not fulfill users requests on actual use.